A general understanding of the principles of the context of the present invention can be found in “Theoretical analysis of numerical aperture increasing lens microscope”, S. B. Ippolito, B. B. Goldger, and M. S. Unlu, Journal of Applied Physics 97, 053105 (2005).
Conventional right angle (90 degree scatter) particle counters employ a planar flow cell and separate collection optics system to detect particles in fluid. The planar flow cell is required so that the surfaces can be highly polished and AR coated to minimize stray light and improve sensitivity. However, this optical configuration results in a limited numerical aperture that can lead to a classical reversal in the response curve as the amount of light actually decreases as particle sizes increase in the Mie regime making the device of little use in this regime. There is a need for an invention that effectively eliminates this problem.
In addition, there is a need for an invention that permits the numerical aperture of the collection system to be increased without introducing spherical aberration thereby allowing the device to detect smaller particles
U.S. Pat. No. 4,728,190 refers to the use of lens in contact with a capillary or flow cell. However, these elements are part of a near forward geometry light scattering instrument (scattered light and light source centered on the same axis). Unlike the present invention, U.S. Pat. No. 4,728,190 applies to a right angle geometry light scattering instrument (scattered light and light source orthogonal to each other).
In addition, unlike the present invention, the primary purpose of the lens/capillary combination in U.S. Pat. No. 4,728,190 is to reduce stray light at the air/glass interface of the face of the capillary or flow cell in the path of the light source. This is not a benefit of the lens/reflector/flow cell combination in the present invention.